A Comprehensive Study on the Ice Freeze-Thaw Process in a High-Elevation Large Lake of the Tibetan Plateau

Abstract

Frozen lakes are common across temperate and subarctic zones of the Northern Hemisphere, including the high-elevation inland lake zone of the Tibetan Plateau (TP), where the freeze-thaw processes are rarely studied due to the harsh environment and limited field experiments. This study, using in situ measurements, satellite products, and the Weather Research and Forecasting with lake (WRF-Lake) simulations at Nam Co, TP, investigates under-ice thermodynamics and lake-atmosphere flux exchange by considering ice surface momentum roughness length $\left(z_{0m}\right)$, solar radiation transmission, and snowfall accumulation. The results indicate that default WRF-Lake simulations reproduce the seasonal variations of ice phenology dynamics and thermal evolution patterns but exhibit excessively slow under-ice warming, premature ice-off, and overestimated sublimation. Eddy covariance (EC) measurements suggest that the typical ice surface $z_{0m}$ value $\left(1.65\times {10}^{-4}m\right)$ is approximately one order of magnitude lower than the default value $\left(1\times {10}^{-3}m\right)$, causing weaker water warming, reduced sublimation, and earlier ice-off. Solar radiation transmission considerably enhances under-ice warming but also advances ice melt. Snowfall accumulation can significantly cool the lake, postpone the ice-off date, prolong the ice-covered period, and substantially reduce sublimation. The simulated under-ice thermal structure, ice phenology, and sublimation can be significantly improved by incorporating the above three thermodynamic processes simultaneously, reducing RMSEs for shallow water temperature and sublimation from 0.93°C and 1.98 mm to 0.71°C and 0.98 mm. This study provides the first comprehensive and detailed analysis of the freeze-thaw process of high-elevation large lakes, showing significance for the numerical simulation of lake water resources and climate impacts.